Whole Soil Sampling to Compare Carbon Sequestration Under Perennial Pastures of Western Australia

Changing from annual to perennial pastures may be a key strategy for farmers to both adapt to, and help mitigate, climate. In this study organic carbon determined by Walkley and Black analysis of 'whole soil' samples (i.e., including ischolar_mains) from annual and perennial pastures was used to determine the carbon stocks in the top 30 cm of soil. Samples were collected from old perennial pasture trial sites, and also from adjoining paired paddocks of annual and perennial pastures. Sequestration rates were calculated as the increase in carbon stocks of the perennials above the traditional annuals, averaged over the number of years since the perennials were sown. The results indicate that denser perennial pastures can sequester in the range of 5 to 10 t CO₂e/ha/year. We hypothesise that the flux rates from particulate organic matter to the humus pool currently used for annuals in RothC may be too low for perennial pastures. These results are particularly encouraging as (a) all but one of the sites was on coarse sandy soils, and (b) all of the years since the perennials were sown were below average rainfall.